Study on the distribution of radioactive trace elements in vitamin D-overloaded rats using the multitracer technique

Biokinetic models for Group VB elements

This paper reviews biokinetic data for the Group VB elements vanadium, niobium, and tantalum, and presents biokinetic models describing their systemic behaviour. The model for systemic niobium in adults was developed earlier and described in Publication 134 of the International Commission on Radiological Protection. The model for niobium is used as a starting point for the development of models for vanadium and tantalum. Published biokinetic data for vanadium, including comparisons with niobium, indicate that the initial distribution of vanadium is broadly similar to that of niobium but that vanadium is less firmly fixed in most tissues and is excreted more rapidly than niobium. Biokinetic data for tantalum are more limited but suggest that its systemic behaviour closely resembles that of niobium at early times after administration. The model for niobium is proposed for application to tantalum in view of the suggested biological similarities of tantalum and niobium, their generally strong coherence in nature due to similar ionic radii and identical valence states, and the difficulties in developing parameter values directly from available data for tantalum. The proposed model for vanadium relies largely on vanadium-specific information and varies considerably from the model for niobium.

Simultaneous production of 28Mg and 47Ca by high-energy heavy-ion irradiation for applications in biology

With the aim of preparing carrier-free 28Mg and 47Ca simultaneously, Ti, V and Fe targets were examined by irradiating with high-energy ions of 12C, 14N and 16O accelerated by the RIKEN Ring Cyclotron. Among the targets, V gave the highest cross section for the formation of both 28Mg and 47Ca irrespective of the kind of beams. The cross section for the formation of 28Mg by the reactions of Ti, V and Fe targets with ion beams increased in the order of 12C < 16O<14N. On the other hand, the three beams exhibited almost the same cross sections for the formation of 47Ca by the reaction of a given target. Titanium and V were selected as prospective targets and 14N as a suitable beam for the production of 28Mg and 47Ca. Chemical separation procedures of the radiotracers in carrier- and salt-free states have been established by using cation exchange resins. The recovery yields of 28Mg and 47Ca from Ti target were 70 and 90%, respectively, and the decontamination factor was less than 10-5. The recovery yields of 28Mg and 47Ca from V target were 80% and the decontamination factor was less than 10-7.

In vivo multitracer analysis technique: screening of radioactive probes for noninvasive measurement of physiological functions in experimental animals

A novel screening experiment, to find radioactive probes for non-invasive measurements of physiological functions in experimental animals, was tested using the in vivo multitracer analysis technique. The details of the efficiency of the detector settings used in the in vivo multitracer analysis technique were examined by both computer simulations and practical measurements. Multiple radioactive isotopes, i.e. multitracer, were prepared by irradiating a silver foil target with a heavy ion beam at the RIKEN ring cyclotron. After chemical separation of the silver target, the multitracer was finally dissolved in isotonic citrate buffer. The multitracer solution was intravenously injected into rats. Using a gamma-ray detector equipped with a well-defined slit, the collimated gamma-rays from the upper abdomen of living rats were measured. After correction of detection efficiencies, it was possible to compare the distribution of radioactive elements between two groups of rats different in body weight. The in vivo measurement showed that the tissue substantial volume of the selenium-deficient (SeD) rat liver increased compared to normal rats. The possibility of a functional estimation of tissue/blood volume for living rats was proposed based on the characteristic in vivo distribution of 74As, 83Rb and 103Ru.

Multitracer Screening: Brain Delivery of Trace Elements by Eight Different Administration Methods

Trace elements are closely associated with the normal functioning of the brain. Therefore, it is important to determine how trace elements enter, accumulate, and are retained in the brain. Using the multitracer technique, which allows simultaneous tracing of many elements and comparison of their behavior under identical experimental conditions, we examined the influence of different administration methods, i.e., intravenous (IV), intraperitoneal (IP), intramuscular (IM), subcutaneous (SC), intracutaneous (IC), intranasal (IN), peroral (PO), and percutaneous (PC) administration, on the uptake of trace elements. A multitracer solution containing 16 radionuclides (i.e., 7Be, 46Sc, 48V, 51Cr, 54Mn, 59Fe, 56Co, 65Zn, 74As, 75Se, 83Rb, 85Sr, 88Y, 88Zr, 95mTc, and 103Ru) was used. The results indicated that the 83Rb brain uptake rate with intranasal administration was approximately twice those obtained with the other administration methods. This result indicated that a portion of Rb was delivered into the brain circumventing the blood circulation and that delivery could be accomplished mainly by olfactory transport. Multitracer screening of trace element delivery revealed differences in brain uptake pathways among administration methods.

[Noninvasive detection of dynamics of various elements in the upper abdomen of selenium-deficient rat using multitracer analysis technique]

The advantages of a technique as a diagnostic tool for examining the distribution of bio-trace elements in the living body are discussed. Time courses of the distribution of Be, V, Mn, Fe, Co, Zn, As, Se, Rb, Sr, and Y in the upper abdomen of living selenium-deficient rats were examined using the in vivo multitracer analysis technique. The dynamics of the elements were estimated by comparison with the distribution of As. Almost all As was taken up by red blood cells. The present findings of a decrease in Se and increase in Co in the liver of Se-deficient rats are in good agreement with the previous data that showed a decrease in Se and increase in Co uptake into the liver cell fraction of Se-deficient rats. Although the normalized uptake rate and the relative distribution of Co 48 h after administration increased in Se-deficient rats, the early level of the relative distribution of Co was not lower compared with that in the normal group. This suggests that the high level of the normalized uptake rate and the relative distribution of Co in Se-deficient rats were affected by the decreasing excretion rate rather than by the increasing uptake rate of Co. The plateau level of relative distribution of Se in the Se-deficient rats is lower than that in normal rats, suggesting that the lower levels of the normalized uptake rate and relative distribution of Se in Se-deficient rats were due to the decreased uptake rate of the element.

Contents and uptake rates of Mn, Fe, Co, Zn, and Se in Se-deficient rat liver cell fractions

The contents of manganese (Mn), iron (Fe), cobalt (Co), zinc (Zn), and selenium (Se) in nuclear (NU), mitochondrial (MT), microsomal (MC), and cytosolic (CS) fractions of liver homogenates of normal and selenium-deficient (SeD) rats were determined by instrumental neutron activation analysis (INAA). The uptake rates of these elements in the liver cell fractions of both groups of rats were determined by multitracer analysis (MTA). The results indicated that Se-deficiency caused a significant increase in the content of Fe in the MC fractions. The MTA showed that the uptake rate of Fe was highest in the MC fraction, and that the uptake rate in the fraction was similar between the SeD and normal rats.

Multitracer techniques: applications in chemical and life sciences

The scope and approaches of the "multitracer technique" have briefly been reviewed. The various aspects of the "multitracer technique" include, the methods of accelerator production of "multitracers" and their separation, the application of this technique in the study of adsorption of metal ions on solid surfaces and in the study of distribution of trace elements in plants and animals.